I mentioned in the post on lavender essential oil that there were two stereoisomers of linalool - what the heck is an isomer?
"Enantiomers are two stereoisomers that are related to each other by a reflection: They are mirror images of each other, which are non-superimposable....They have the same physical properties, except for the direction in which they rotate polarized light and how they interact with different optical isomers of other compounds. As a result, different enantiomers of a compound may have substantially different biological effects." (Wikipedia) In other words, they have the same molecular formula, but differ in their structure by being reflections of the other. As you'll see in the next example, they might look very similar but we can have different reactions to them!
linalool, we noticed that there are two stereoisomers of linalool - licareol or (R)-(-)-linalool found in lavender, bay laurel, neroli, bergamot, and sweet basi,l and coriandrol or (S)-(+)-linalool found in coriander, palmarosa, petitgrain, and sweet orange flowers.
We also noticed that one stereoisomer had an R and - in front of the name and the other had an S and + in front of its name. These letters/symbols indicate that these are enantiomers. The R and S designation are based on the Cahn–Ingold–Prelog priority rules (CIP), based on atomic number. (Click here to read more about how these are named. It's a bit detailed for this post!) The + and - in the name relates to optical activity. "An enantiomer can be named by the direction in which it rotates the plane of polarized light. If it rotates the light clockwise (as seen by a viewer towards whom the light is traveling), that enantiomer is labeled (+). Its mirror-image is labeled (−). "
You might hear these molecules being described as chiral - a molecule that "lacks an internal plane of symmetry and thus has a non-superimposable mirror image." (Wikipedia)
And if you want to know more about naming chiral molecules, click here!
Wikipedia) These limonene enantiomers have different effects on us: The D-limonene has a clean, citrus-y odour, whereas the L-limonene has a piney, turpentine-like odor.
If you want to learn more about isomers and chirality, click on this WikiBooks link for a much more detailed write up!
Do you need to know this stuff to know more about essential oils? No, but it's interesting, eh?